A standard hypodermic syringe has a cylindrical body having a front end fitted with a cap in turn carrying a needle that projects along the axis of the body into the body and a rear end sealed by a piston carried on a plunger. The plunger is pressed forward to pressurize a liquid in the body and force it forward out of the body through the needle.
To meet current hygienic standards it is nowadays standard to make such a hypodermic assembly as a throwaway item intended for only a single use. Thus it must be made at the lowest possible cost. At the same time the hypodermic must be certain to work perfectly, and must be protected against or at least provide a visual indication of tampering or an unhygienic condition.